FR2503388A1 - CONNECTOR END FOR OPTIC FIBER, METHOD FOR CENTERING FIBER THEREIN AND DEVICE FOR IMPLEMENTING SAID METHOD - Google Patents

Abstract

THE PRESENT INVENTION CONCERNS A TIP 4 OF A FIBER OPTICAL CONNECTOR, A METHOD FOR CENTERING THIS FIBER AS WELL AS A DEVICE FOR CENTERING THE FIBER IN THE TIP. ACCORDING TO THE INVENTION, THE TIP 4 INCLUDES A SLEEVE 15 ON WHICH A CENTER 20 OF CORRESPONDING INTERNAL SHAPE IS POSITIONED, HAVING A CYLINDRICAL OPENING 21 IN WHICH FIBER 2 IS LODGED. COMMUNICATES WITH THE INTERNAL CYLINDRICAL CHANNEL 5, 7, 8 OF THE NOZZLE 4, IN WHICH A POLYMERISABLE RESIN 10 IS CAST WHILE THE FIBER IS HELD IN PLACE BY THE CENTER. AFTER POLYMERIZATION, THE END OF THE TIP IS POLISHED USING A SUITABLE TOOL. APPLICATION: CONNECTORS FOR OPTICAL FIBER.

Description

CONNECTOR FIT FOR OPTICAL FIBER,

  METHOD FOR CENTERING A FIBER IN THIS TIP

  AND DEVICE FOR IMPLEMENTING SAID METHOD

  The present invention relates to a connector tip for optical fiber having a cylindrical centering sleeve, in which is pierced a cylindrical channel allowing the passage of the

  fiber, said centering sleeve having at its anterior end

  a contact face o opens said fiber. It also relates to a method of centering the fiber in this mouthpiece and

  that a device for the implementation of this centering method.

  It is known, for example from US Pat. No. 4,193,664, to produce connector tips for optical monofibre, such tips being intended for connecting the fibers together. The problem that currently arises in the realization of these single-channel fiber optic connectors is the centering of the fiber in the tip allowing a transmission of light with minimal losses at the connection. In the US patent cited above, the tip comprises in particular two V-shaped reference planes with respect to which the optical fiber is

  positioned. For this purpose, a centering device comprising a

  for example, two V-shaped planes complement each other

  the fiber itself is positioned in a groove formed by two planes parallel to the previous V-shaped and arranged respectively at very precise distances from each other. The fiber is then immobilized with the aid of a polymerizable resin in the endpiece and the latter is removed from said positioning means and after polishing.

  the end of the tip, it is ready for use.

  However, such a process has a number of

  vantages. In particular, the tip must have two planes forming a V and having a very precise angle to respect one with respect to the other. This is quite difficult to achieve and the tips used in this technique are, therefore, a high cost. Moreover, during the centering of the fiber, it is necessary to strongly apply the reference planes of the tip against the referencce plans of the apparatus and the operations thus carried out must be performed with great care. Although this technique gives overall satisfaction, there are many cases where one can be satisfied with a less important precision than that reached with it, insofar as the solution implemented

  is much simpler to achieve.

  The connector tip for optical fiber according to the invention avoids these disadvantages. For this purpose, it is characterized in

  it comprises on the one hand a radial cylindrical hole which communicates

  with the cylindrical channel and a centering sleeve disposed towards its rear end, the fiber being maintained substantially parallel to the axis of the cylindrical channel, firstly in the rear part of the endpiece by 14 centering sleeve, and on the other hand in the front part of the sleeve by a polymerized resin, introduced before polymerization by the cylindrical hole

  radial and which keeps the fiber in this position after polymeric

tion.

  According to a preferred embodiment, the connection tip

  fiber optic transmitter according to the invention is characterized in that the sleeve has a chamfer arranged near the end

front of the cylindrical channel.

  The invention also relates to a method of centering a

  optical fiber in a tip as described above. According to the invention

  tion, the sleeve disposed at the anterior end of the tip is

  coated with a centraliser having a cylindrical inner shape complete

  of the sleeve and pierced at its center with an opening

  cylindrical diameter substantially equal to that of the fiber to be centered. We then introduce into the cylindrical channel of the mouthpiece the

  optical fiber, which is then slid into the cylindrical opening

  t503588 dries the locator, crossing it on both sides. Since the sleeve has very precise external dimensions and the centering device has very precise internal dimensions, as well as a very precise position of the cylindrical opening relative to the cylindrical internal walls complementary to that of the sleeve, the optical fiber is thus perfectly centered in the sleeve. Then, through the radial cylindrical hole, a polymerizable liquid resin is introduced into the cylindrical channel, said resin being surrounded by its appropriate fluidity, the optical fiber optionally provided with a sheath. The polymerizable resin being selected from thermosetting resins that polymerize very rapidly at room temperature, the fiber is thus quickly and permanently centered in the tip. In order to avoid a pollution of the centraliser by the resin, the front end of the cylindrical channel of the sleeve is provided with a chamfer forming a small cavity at the end of the sleeve. This chamfer is preferably constituted by a cylindrical shape of diameter greater than the diameter of the cylindrical channel. This makes it possible in particular to prevent the resin from extending substantially beyond the anterior face of the sleeve. Furthermore, the tip is provided on the one hand, and the centralizer on the other hand, abutments that cooperate with each other so as to leave a space between the anterior face of the sleeve and the bottom of the cavity

  cylindrical inner of the centraliser.

  Moreover, the cylindrical opening disposed substantially in the center of the cylindrical cavity of the centraliser itself has a

  chamfer intended to facilitate the introduction of the optical fiber.

  In order to prevent the fiber being perfectly centered in the cylindrical opening of the centralizer, but slightly offset from the center of the cylindrical channel at the anterior face of the sleeve, the end of the connector is provided near its rear end. a centering sleeve of sufficient length which substantially maintains the fiber in the axis of the cylindrical channel and which cooperates with the cylindrical opening of the centraliser

  to achieve further improved centering of the fiber in the tip.

  When the resin used is polymerized, the centering device is then removed from the sleeve. A drop of resin, preferably identical to the resin already used, is then deposited in the cylindrical chamfer located towards the anterior face of the sleeve. In this way, the resin chamfer is thus completely filled, the latter being placed in sufficient quantity to produce a resin cone disposed above the anterior face of the mouthpiece and

having as its axis the optical fiber.

  The sleeve is then coated with a polisher having a central opening having the same internal dimensions, to

  tolerances close, than those of the sleeve. This one comes then

  by its anterior surface the flat face of the polisher. So that the alignment of these two faces is perfect and corresponds to the conditions of use, this polisher is provided with fixing means complementary to those of the tip. The dimensions of the polisher are then calculated so that when these fastening means are assembled, the anterior face of the sleeve and the flat face of the polisher are strictly aligned. The polymerized resin cone surrounding the fiber then protrudes well above the plane face of said polisher; the fiber and resin assembly is then rectified by alignment on the flat face of said polisher. Thus, after separation of the polisher and the tip, a tip in which the optical fiber is perfectly centered, and whose end

  is perfectly aligned with the anterior face of the sleeve.

  The invention will be better understood with the aid of the following exemplary embodiments, given in a non-limiting manner, together with the figures which represent: FIG. 1, a connector endpiece according to the invention for an optical monofiber, the end of which the sleeve FIG. 2 is a view of the centralizer according to the invention, FIG. 4 is a diagrammatic view explaining the role of FIG. the

centering sleeve of the mouthpiece.

  In Figure 1, there is shown the first step of the method according to the invention which consists in centering the fiber in the tip and casting a polymerizable resin in the central cylindrical channel thereof. The optical cable 1 comprises an optical fiber 2, possibly

  coated with its optical sheath, and a protective sheath 3.

  This sheath may be either a coating or possibly the optical sheath itself in the case where it is a flexible sheath of the silicone type. The optical fiber 2 is disposed in the central cylindrical channel of the nozzle 4, a channel successively composed of

  several parts of decreasing diameters from the posterior part

  towards the anterior part of the mouthpiece. The posterior portion 5 of this cylindrical channel is of relatively large diameter relative to the diameter of the fiber coated with its sheath to allow the housing of the centering sleeve 6 to be housed. It continues with a central portion 7 of smaller diameter, itself even continuing with an anterior portion 8 of diameter little greater than the outer diameter of the fiber coated with its sheath. The tip 4 has at its front part the centering sleeve 15 itself. This cylindrical shape has precise external dimensions as a reference. The cylindrical channel 8 is perfectly centered with respect to the axis of the sleeve 15, within the limits of acceptable tolerances. This sleeve 15 ends with a chamfer 14 which connects its cylindrical wall 25 to the front face 13 of said sleeve. This anterior face is itself perfectly flat and perpendicular to the axis of the sleeve 15. This ends at the level of the face

  former 13 by an internal chamfer 12 composed of a cylindrical portion

  prolonged drique towards the inside of the cylindrical channel by a conical portion joining said channel, which facilitates the machining of this form. Preferably, it has been found that the best results are obtained when this conical part of the chamfer did not exist, that is to say when it had a cylindrical shape. In this embodiment, the endpiece 4 also has near the sleeve 15 but not on it, a radial cylindrical hole 9 which communicates with the anterior cylindrical channel 8 and with the central and rear portions 7 and 5 of the channel. The tip 4 also has cavities 49 for housing a seal and sleeve not shown in the figure to give it the characteristics well known to those skilled in the art of the connectors.

type "SMA".

  On the sleeve 15, the centralizer 20 is positioned. This latter has a cylindrical internal cavity of identical diameter to the

  outside diameter of the reference cylinder 15, within tolerances.

  The inner walls of this centraliser are also represented on

  the figure by the reference 25 as the outer walls of the sleeve 15.

  This internal cavity of the centraliser is extended towards the posterior part

  first of it by stops 26 which cooperate with the corresponding stops 24 of the nozzle 4. These stops 24 at the tip 4 are simply formed by a flange of diameter greater than the diameter of the reference cylinder 15. The stops 26 are constituted by the planes perpendicular to the axis of the centralizer cavity. The depth of the internal cavity of the centralizer is slightly greater than the length of the sleeve 15: when the stops 24 and 26 come into contact with one another, the anterior face of the sleeve 15 and the bottom 23 of the internal cavity of the centraliser are at a distance from each other equal to d. In practice, a distance d of the order of 0.1 mm has been particularly

satisfactory.

  The cylindrical opening 21 disposed exactly in the center of the cylindrical cavity of the centralizer and passing therethrough from its face 23 to its face 27, is provided with a chamfer 22

  allowing an easier introduction of the fiber 2.

  The elements being arranged as described above and as shown in FIG. 1, a liquid resin is introduced.

  polymerizable in the opening 9, the latter spreading partially

  7 as a chamfer 11 at the end of said channel 8. As polymerizable resin, any resin well known to those skilled in the art for this type of embodiment will be used. In particular, it will choose, depending on the diameter of the openings, the nature of the fibers used and their sheaths, ... and generally all the relevant parameters, a polymerizable resin or glue of fluidity adapted to behave in the manner described above. This can be achieved by simple routine manipulations with commercially available polymerizable resins. In particular, the epoxy resins or

  epoxy glue well known to those skilled in the art, mono or bi-component

  as well as acrylate-type glues. In particular, the resins which polymerize at room temperature in a very short time of the order of a few minutes will be used. When the polymerization is carried out, the centraliser is then removed from

the tip 4.

  The following operation is to fill the chamfer 12 with a drop of resin as described above, so as to form substantially a cone above the contact face 13 of the sleeve 15. The following operations is then shown in Figure 2, in which the same elements as those of Figure 1 have the same references. The tip 4 has been coated with the polisher 50. This polisher comprises an inner cylindrical channel of the same dimensions with tolerances as the outer dimensions of the sleeve 15. This cylindrical channel opens on the anterior face 51 of the polisher 50. This comprises stops 35 that come

  cooperate with the stops 24 of the nozzle 4. These stops are position-

  in such a way that the anterior face 13 of the sleeve 15 is exactly aligned with the anterior face 51 of the polisher 50. The polisher 50 has a thread 32 which cooperates with the ring 30 secured by means of the seal 32 of the mouthpiece 4. The tip provided with its ring is a connector tip well known to those skilled in the art under the reference "SMA". The ring 30 has a body 31 also having a threaded inner portion which cooperates with the thread 32 of the polisher 50. These different threads

  allow to bring rigorously into abutments and to maintain

  The drop of cone-shaped resin 40 which is disposed above the chamfer 12 of the channel 8, is then rectified using the means well known to those skilled in the art, to perfectly align the front end 13 of the sleeve 15, the resin and the optical fiber 2. After this operation which does not pose any particular difficulties, the polisher is then

  removed from the tip that is ready for use.

  FIG. 3 represents a detailed view of the centraliser according to the invention, the same elements as those of the preceding figures bearing the same references. This centralizer 20 has a cylindrical inner shape 61, complementary to that of the sleeve 15, having an axis of symmetry identical to that of the cylindrical opening 21. Moreover, the dimensions of the inner walls 25 and those of the sleeve 15 being very close and adjusted, it is necessary to provide a complementary opening 60 for the evacuation of air during the maneuver penetration of the sleeve in the centraliser. FIG. 4 represents a very schematic view of a mouthpiece

  in which one would not have provided the centering sleeve 6. Schémati-

  The fiber 4 is not held by the centering sleeve 6, its axis 66 necessarily has a certain inclination with respect to the axis of the cylindrical channel 8. According to the tolerances on the fiber and on the hole 21, this angle can be variable and cause relatively large centering errors. Thus, in Figure 4 where these errors have been greatly exaggerated, we see that the center 67 of the channel 8 at the anterior face 13 of the sleeve is not coincidental with the center 68 of the fiber at this level. Therefore, if the other end to which it will be connected has the same centering error but in the other direction, one can

  have transmission losses at the relative connection-

  important; this is why the centering sleeve 6 according to the invention is particularly necessary if a good quality connection is to be obtained: it is possible in all cases to improve the optical transmission by providing polarization means on

  each endpiece when mating in a connector.

  Depending on the case, the person skilled in the art will use optical fibers

  to implement the invention, coated or not with their optical cladding and coated or not with a surface protection coating. When using hard fibers, that is to say hard-sheath fibers, glass-glass or silica-silica type, it is understood that the optical sheath is necessarily maintained over the entire length of the fiber. Since these fibers are generally coated with a coating of a relatively flexible polymer, this may be retained if this coating is sufficiently concentric.

  compared to the fiber optic sheath for the intended application.

  Gee. In the opposite case, the stripping of the fiber will be done in such a way that this coating does not exceed the zone 7 of the cylindrical channel of the end-piece 4. When fibers with flexible sheaths are used, reference can be made to the sheath if it is sufficiently concentric, either take reference directly on the fiber. In the latter case, it will be arranged to remove this optical sheath at the end of the fiber 2, so that only the core of the fiber itself is introduced into the cylindrical opening 21 which will have the appropriate dimensions . To ensure a good connection, the optical sheath will be maintained on the fiber up to the level of the

  surface 23, above the anterior face 13 of the sleeve 15.

Claims (9)

  An optical fiber connector (4) having a cylindrical centering sleeve (15), in which a cylindrical channel (5, 7, 8) for the passage of the fiber (2), said centering sleeve ( 15) having at its front end a contact face (13) o opens said fiber (2), characterized in that   it comprises on the one hand a cylindrical-radial hole (9) which   with the cylindrical channel (5, 7, 8) and a centering sleeve (6) disposed towards its posterior end, the fiber (2) being maintained substantially parallel to the axis of the cylindrical channel (5, 7, 8). ) on the one hand in the rear part of the nozzle (4) by the centering sleeve (6), and on the other hand in the front part of the reference cylinder by a polymerized resin (10), introduced before polymerization by the radial cylindrical hole (9) and which   keeps the fiber in this position after polymerization.   2. connector connector for optical fiber according to the   cation 1, characterized in that the sleeve (15) has a chamfer   (12) disposed near the anterior end of the cylindrical channel that (8).   3. A method of centering a fiber in a ferrule comprising a sleeve (15), in which a cylindrical channel (5, 7, 8) is pierced, characterized in that the sleeve (15) is introduced into a centralizer (20). ) of cylindrical inner shape complementary to that of the sleeve (15) and pierced at its center with a cylindrical opening (21) of diameter substantially equal to that of the fiber to be centered, the latter being introduced into the cylindrical channel (5, 7, 8) and then the cylindrical opening (21) so as to be centered with respect to said channel (5, 7, 8), a liquid polymerizable resin (10) being introduced   then in this channel, said centraliser being removed after polymerization resin.   4. Method according to claim 3, characterized in that it maintains a sufficient distance between the anterior end of the sleeve and the bottom of the centraliser, so as to avoid the contact of the resin and centraliser.   5. Method according to one of claims 3 or 4, characterized in   the centralizer (20) has external stops (26) which   come into contact with the corresponding stops (24) of the end piece (4).   6. Method according to one of claims 3 to 5, characterized in   the sleeve has a chamfer (12) disposed near the forward end of the cylindrical channel, said chamfer being filled with polymerizable resin to form a cone   protrusion (40) relative to the anterior face (14) of the sleeve.   7. Method according to one of claims 3 to 6, characterized in   what is then adjusted on the sleeve a polisher (50) comprising   both a flat face (51), said polisher being pierced with a central opening in which penetrates the sleeve (15) which is flush with its front face the flat face of said polisher, the resin (10) and the fiber (2) arranged protruding from the plane face and the anterior face aligned with each other, being ground and   brought in the same plane as said faces.   8. Centraliser for the implementation of the method according to one of the   Claims 3 to 7, characterized in that it comprises a shape   cylindrical interior (61) complementary to that (25) of the sleeve (15) with which it cooperates, the base (23) of the centralizer being pierced at its center with a cylindrical opening (21) of diameter substantially equal to that of the fiber (2) to center and oriented parallel to the axis (62) of the cylinder.   9. Centraliser according to claim 8, characterized in that it also comprises an opening (60) connecting the base of the inner cylinder and the anterior face of the centralizer, allowing the evacuation   air during the centering operation.